Previously proposed packet data switches would appear to be burdened with one or more of the disadvantages set forth below.
It has been a problem with transferring a data packet from an incoming data link to several outgoing data links, so-called broadcasting or multicasting. In certain cases this has only been achieved using relatively complicated special arrangements, e.g. so-called copying networks for copying data packets. It has not always been possible to assign a data packet different channel numbers on different outgoing data links when a data packet is transferred to several outgoing data links. However, it is an advantage if it is possible to assign such a data packet different channel numbers on different outgoing links, since it is not certain that one channel number which is utilized for a data packet on an incoming link can also be utilized for the same data packet on all outgoing links.
With previously proposed packet data switches, it has not always been possible to maintain the chronological order between several incoming data packets.
A design with a common control memory for several data links results in that a time multiplex method must be applied. A prerequisite for this is that the control memory must be able to work very rapidly if the selector is to be able to handle high data speeds.